A fuel cell system is an electricity generating system which directly converts the chemical reaction energy of oxygen and hydrogen contained in a hydrocarbon material such as methanol into electrical energy.
A fuel cell system often uses hydrogen generated by reforming methanol or ethanol as the fuel, and has a wide range of applications which include mobile power sources for vehicles, distributed power sources for homes or buildings, and small-sized power sources for electronic apparatuses.
A fuel cell system basically includes a stack, a fuel processing unit, a fuel tank, and a fuel pump. The fuel processing unit includes a reformer which reforms the fuel through a catalytic reforming reaction using thermal energy to generate a reforming gas containing hydrogen, and a carbon monoxide purifier which reduces the carbon monoxide concentration of the reforming gas by preferentially oxidizing the carbon monoxide. One example of a carbon monoxide purifier is a preferential CO oxidation (PROX) reactor which is well-known in the art.
In the fuel cell system, the fuel pump operates to supply the fuel stored in the fuel tank to the reformer. The reformer reforms the fuel to generate the reforming gas. The carbon monoxide purifier reduces the concentration of carbon monoxide contained in the reforming gas.
The reforming gas in which the concentration of carbon monoxide has been reduced is supplied to the stack along with air supplied through an air pump. In the stack, an electrochemical reaction of the oxygen contained in the air and the hydrogen contained in the reforming gas generates electrical energy.
However, in a conventional fuel cell system, the reformer cannot completely reform the entire fuel, and thus, a non-reactive component of the fuel is discharged along with the reforming gas. The reforming gas and the non-reactive fuel component are transferred from the reformer to a carbon monoxide purifier.
In the carbon monoxide purifier, the non-reactive portion of the fuel may oxidize with oxygen, generating unnecessary heat. The unnecessary heat can reduce the activity of the PROX reaction in the carbon monoxide purifier. In addition, a methane forming reaction may occur, consuming the reforming gas, or the carbon monoxide purifier may be damaged.